I always try to use the Great Khan armorer when I need to sell stuff and buy ammo. She usually doesn't have a ton of caps, but she has a ton of ammo and a reloading bench in her room. The good part is she buys your stuff at retail price. I usually buy a ton of ammo to give her caps and sell all my stuff to her for retail.

Lol I know how you feel, with hunting rifles and shotguns I get all the mods straight away.
So I thought the same would happen for lasers when I tried an EW build, I did'nt want to use the restock glitch, not a mod showed up till level 16+.
Then all the merchants stocks froze with the same base items, so now if I have the caps I just quit and reload for a main weapon.

Crimson caravan, the Arms dealer at the 188, and even the Dinky shop are the most reliable, if not the gun runners.
For the CC / Dinky just enter the interior cell, don't save and check out blakes wares, if none in quit to main menu and continue from the auto save.

Are the prices adjusted by your level or the amount of caps you have (or stimpacks)? Last night all the stimpacks jumped in price from 27-35 caps to 100-110 caps. Superstims are still about 130. I guess I'll buy them from now on.

And last night when I wanted to sell things to the wandering trader outside of Novac he only had 200 caps. The last time I sold to him, I only sold 1K worth of stuff. He didn't have much on him either.

The new patch changed the stimpak prices.

Thanks Snowy! I just read that elsewhere. It does make sense. Those things would be highly desired. Good thing my character can make them.